Stabilized acrylonitrile polymers



United States Patent 2,813,845 STABILIZED ACRYLONITRILE POLYMERS George L. Wesp, Englewood, and Robert I. locombe,

Dayton, Ohio, assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application June 12, 1953, Serial No. 361,438

9 Claims. (Cl. 26045.75)

This invention relates to methods of preparing polymers of acrylonitrile which are stabilized with respect to thermodiscoloration. More specifically the invention relates to methods of converting unstable polymers of acrylonitrile into color-stable polymers.

Although polyacrylonitrile and eopolymers of 50 percent or more by weight of acrylonitrile and other monomers containing olefinic unsaturation copolymerized therewith, are generally regarded as being materials of good thermostability, they are subject to discoloration. This phenomenon generally results because of the need for extruding and molding the composition at elevated temperatures. Furthermore the higher acrylonitrile polymers find extensive use in the fabriaction of fibers, films and fabrics which frequently are subjected to ironing operations at elevated temperatures. Thus, serious discolorations are often developed in the fabrication and processing of acrylonitrile polymers.

The primary purpose of this invention is to provide color-stable polymers of acrylonitrile. A further purpose of the invention is to facilitate molding and other processing procedures usually encountered at elevated temperatures. A still further purpose of the invention is to provide substances which can be added to conventional polymers to induce resistance to heat and discoloration.

It has been discovered that by adding specific inorganic salts of magnesium to acrylonitrile polymers improved resistance to discoloration may readily be developed. The nature of the chemical reaction involved is not definitely understood, but it is believed that the color change is due to some impurities present in the polymer. It may be that the magnesium ions react with the impurity to form a substance which is more heat-stable than the impurity in its original form. Since not all magnesium compounds produce the same degree of beneficial effect the phenomena apparently involve additional stabilization by the anion as well as the cation. The total stabilization may involve additive or synergistic effects. Irrespective of the mechanism, it has been found that specific magnesium salts produce the desired effect.

The acrylonitrile polymers with which this invention may be practiced include polyacrylonitrile and copolymers of from or more percent acrylonitrile and up to 80 percent of one or more of a wide variety of other unsaturated substances known to be copolymerizable with the acrylonitrile. Thus, the invention is practicable with the wellknown fiber-forming copolymers of acrylonitrile, which may be the copolymers of 75 percent or more percent of acrylonitrile and up to percent of other monomers. Other copolymers of from 25 percent to 75 percent acrylonitrile and 75 to 25 percent of the various other monomers, which eopolymers have primary utility in the field of film and molding composition production, are also useful.

The said other monomers with which the acrylonitrile may be copolymerized to produce resinous substances capable of use in the practice of this invention include vinyl acetate and other vinyl esters of monocarboxylic acids having up to four carbon atoms in the carboxylic acid radical, dimethyl maleate and dimethyl fumarate and other alkyl esters of fumaric and maleic acids, wherein the alkyl radical has'up to four carbon atoms, methyl methacrylate or acrylate and other alkyl acrylates and alkyl methacrylates wherein the alkyl radical has up to four carbon atoms, vinyl chloride and other vinyl halides, styrene, alpha-methylstyrene and other vinyl and isopropenyl substituted aromatichydrocarbons, methacrylonitrile, vinylidene chloride, vinylpyridine, the vinyl derivatives of other alkyl substituted pyridines, andthe vinyl derivatives of other compounds containing a tertiary amino atom in a heterocyclic ring, vinyl'chloroacetate and other vinyl esters of haloacetic acids, methallyl, chloroacetate, allyl chloroacetate and chloroallylchloroacetate, and the corresponding esters of other haloacetic esters, vinylimidazole and other N-vinyl derivatives of heterocyclic nitrogen compounds, and one or more of these and other unsaturated compounds known to be copolymerizable with acrylonitrile.

The magnesium salts which are useful in the practice of this invention include magnesium chloride, magnesium sulfate and magnesium nitrate. In the practice of this invention the magnesium salt may be used to the extent of 0.01 percent to ten percent by weight of the acrylonitrile polymer to be stabilized. Preferred practice of this invention involves the use of 0.1 percent to three percent of the stabilizer.

The invention may be practiced by combining the acrylonitrile polymer and the magnesium salt by a wide variety of mechanical procedures. Thus, the polymer may be treated in granular solid form and mixed physically with the solid magnesium salt or an aqueous or other liquid solution or dispersion of the magnesium salt. The physical mixture may take place at room temperature or at higher temperatures, for example the temperature at which the polymer is semi-solid or fluid. A preferred practice involves the use of solvents or plasticizers for the acrylonitrile polymers in the presence of which the intimate dispersing of the stabilizing additive and the acrylonitrile polymer is more readily effected. The nature of the solvent which is useful in dissolving or softening the acrylonitrile polymer will to a large extent depend upon the chemical composition of the acrylonitrile polymers.

The copolymers of percent or more of acrylonitrile and up to 25 percent of the comonomer are well-known fiber forming compositions and are generally resistant to the effect of most chemical solvents. In the preparation of solutions of such copolymers, solvents, such as N,N- dimethylformamide, N,N-dimethylacetamide, gamma-butyrolacetone, ethylene carbonate, maleic acid, alphacyanoacetamide, and tris(dimethylamido)phosphate may be used.

In the treatment of the more soluble types of acrylonitrile polymers, for example those of from 20 percent to 75 percent acrylonitrile and from 25 percent to percent of other monomers copolymerizable therewith, the selection of a solvent is less critical. This type of copoly mer may be dissolved or otherwise physically effected by the various ketones, esters and aromatic hydrocarbon types of solvents. In general, the copolymer is placed in a suitable solution, or softened and swelled by the selected medium so as to enable a more ready dispersion of the magnesium salt within the solid polymer. Obviously a solvent which is also capable of dissolving at least to some extent the magnesium salt to be used will be exceptionally beneficial. However, the selection of the dispersing agent, the stabilizing agent and the particular method of dispersing the salt in the solid polymer is a matter readily determined by one skilled in the art.

To evaluate the stabilizing action of various compounds, acrylonitrile polymers of difierent chemical and physical properties were used and the magnesium salts dispersed therein by a variety of methods.

Example micron filter in the photometer.

Magnesium chloride +26.6 Magnesium nitrate +126 Magnesium sulfate +233 The present application is ,a continuation-in-part of copending application Serial No. 192,347, now abandoned, filed October 26, 1950.

What we claim is:

1. A stable acrylonitrile polymer comprising a polymer of percent to 100 percent of acrylonitrile and up to 80 percent .of another monoolefinic monomer copolymerized therewith, said polymer containing intimately dispersed therein from 0.01 to ten percent of a magnesium salt selected from the group consisting of magnesium chloride, magnesium sulfate and magnesium nitrate.

2. A stable acrylonitrile polymer comprising a polymer of 20 percent to 100 percent of acrylonitrile and up to 80 percent .of another monoolefinic monomer copolymerized therewith, said polymer containing intimately dis persed therein from 0.1 to three percent of a magnesium salt selected from the group consisting of magnesium chloride, magnesium sulfate and magnesium nitrate.

3. A stable acrylonitrile polymer comprising a polymer of 20 percent to 100 percent of acrylonitrile and up to percent of another monoolefinic monomer copolymerized therewith, said polymer containing intimately dispersed therein from 0.01 to ten percent of magnesium chloride.

4. A stable acrylonitrile polymer comprising a polymer of 20 percent to percent of acrylonitrile and up to 80 percent of another monoolefinic monomer copolymerized .therewith, said polymer containing intimately dispersed therein from 0.1 to three percent of magnesium chloride.

5. A stable acrylonitrile polymer comprising a polymer of 20% to 100% of acrylonitrile and up to 80% of another monoolefinic monomer copolymerized therewith, said polymer containing intimately dispersed therein from 0.01% to 10% of a magnesium nitrate.

6. A stable acrylonitrile polymer comprising a polymer of 20% to 100% of acrylonitrile and up to 80% of another monoolefinic monomer copolymerized therewith, said polymer containing intimately dispersed therein from 0.1% to 3% of magnesium nitrate.

7. A stable acrylonitrile polymer comprising a polymer of 20% to 100% of acrylonitrile and up to 80% of another monoolefinic monomer copolymerized therewith, said polymer containing intimately dispersed therein from 0.01% to 10% of magnesium sulfate.

8. A stable acrylonitrile polymer comprising a polymer of 20% to 100% of acrylonitrile and up to 80% of another monoolefinic monomer copolymerized therewith, said polymer containing intimately dispersed therein from 0.1% to 3% of magnesium sulfate.

9.. A stable acrylonitrile polymer comprising a polymer of 20% to 100% of acrylonitrile and up to 80% of another monoolefinic monomer copolymerized therewith, said polymer containing intimately dispersed therein from 0.01 to 10% of a magnesium salt selected from the group consisting of magnesium chloride, magnesium sulfate and magnesium nitrate.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A STABLE ACRYLONITRILE POLYMER COMPRISING A POLYMER OF 20 PERCENT TO 100 PERCENT OF ACRYLONITRILE AND UP TO 80 PERCENT OF ANOTHER MONOOLEFINIC MONOMER COPOLYMERIZED THEREWITH, SAID POLYMER CONTAINING INUMATELY DISPERSED THEREIN FROM 0.01 TO TEN PERCENT OF A MAGNESIUM SALT SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM CHLORIDE, MAGNESIUM SULFATE AND MAGNESIUM NITRATE. 